A rotary system typically comprises a rotating element such as a shaft connected to a rotatable device at a force-engagement or working portion thereof and to a driving mechanism at a drive end thereof. The rotary system further comprises one or more bearing assemblies for radially and axially supporting the shaft along its length and typically straddling the working portion. During operation, the shaft is subjected to lateral forces at its working portion about which the rotatable device is connected. This causes some angular deflection of the shaft from its normal rotating axis. In instances where the shaft is supported between at least two closely spaced support bearings, such as a simply supported beam or where one end is constrained and the other simply supported, the angular deflection of the shaft from its normal rotating axis is contained and is small. Support bearings, typically capable of merely radial loads, are not adversely affected by the angular misalignment.
However, the deflection is more pronounced in instances where it is not convenient or economical to provide a second support bearing (a cantilever arrangement) or where it is not possible to closely space the support bearings. In both instances, significant misalignment between the shaft's rotating axis and the axis of the bearing housing can occur. Conventional support bearings cannot accommodate such significant misalignment and this results in failure, accelerated wear and tear of the support bearing or expensive requirement to install spherical bearings.
One example of a challenging environment for shaft support is in the case of a hydroelectric turbine system 10. As illustrated in FIGS. 1A, and 1B, a prior art hydroelectric turbine system 10 is placed within a suitable flow of power fluid, such as water W flowing in a river, penstock, sluice gate or the like. A shaft 14, mounted for rotation about an axis of rotation S, rotatably connects a turbine 16, supported at a working portion 18 thereof and submerged in the flow of water W, with an energy device such as a generator 20 connected at a proximal or non-working end 22 thereof and positioned above the surface of the water. The shaft 14 is radially and axially supported by a radial bearing 24 generally located about an outboard end of the shaft's working portion 18. The radial bearing 24 just happens to also be submerged in the power fluid or water W. The shaft 14 is typically constrained between a pair of bearings at the generator 20.
As shown in schematic format in FIG. 1C, during operation, the fluid imposes a lateral force F on the shaft's working portion 18, causing angular deflection of the shaft 14 and, therefore, misalignment between a rotating axis S of the shaft 14 and an axis X of the structure supporting the bearing 24. The shaft 14 is represented as a beam arrangement, being constrained at the generator 20, typically fit with a spaced pair of bearings, and simply supported at the radial bearing 24.
As shown in FIG. 1D, deflection of the shaft 14 can be even more pronounced when the shaft is cantilevered from the non-working end 22, such as being supported by the generator 20. If the working portion 18 is to be spaced any practical distance from the generator 20, the supporting bearings have to be robust and control significant misalignment-related behavior.
In order to overcome the misalignment problem, it has been known to use self-aligning bearing assemblies, such as spherical bearing 24 depicted in FIG. 1C, to support the rotating shaft 14 at its working end where the axis of the shaft is misaligned from the axis of the bearing. One such bearing assembly is disclosed in U.S. Pat. No. 8,613,554 to Tessier et al. (US'544 patent) in the context of a hydroelectric turbine system. The self-aligning bearing assembly described in the US'544 patent comprises an inner bearing, an inner bearing support, an outer bearing and an outer bearing support housed in a stationary bearing housing. A spherical joint is located between the outer bearing support and the stationary bearing housing. As represented in FIG. 1C, the spherical joint permits the shaft-bearing inner component of the bearing assembly 24 to tilt or move angularly along with the shaft 14 under load conditions for maintaining bearing support despite angular rotation of the inner bearing and outer bearing.
The bearing assembly of the US'554 patent is, however, complex in nature, includes a large number of components and is, therefore, expensive and difficult to install and maintain.
There is a need in the industry for improved arrangements for overcoming the misalignment problems discussed in the foregoing paragraphs.